I very recently started work at a new hospital as part of a yearly rotation while in training. This hospital has a fire board with the names of staff, followed by two small circles containing the words IN and OUT, and a tiny black magnet that closely resembles a knight from a portable chessboard. The idea, at least at first glance, seems deceptively simple.

Two days into my new job, a junior colleague and I were heading to the wards to review a patient when he stopped at the board and moved the magnet beside his name from the IN circle to the OUT circle. To my eyes, this now indicated that he was in. I pointed this out to him while moving my own little magnetic black knight in the opposite direction. With a self-deprecating smile, my colleague said that he had got the concept wrong, copied what I had done, and we carried on with our duties. I thought little more of it.

A few days later, however, we had a fire tour as part of the induction program for newcomers and, unsurprisingly, the tour culminated in front of the fire board. A foundation year doctor, only days into her life as a practicing doctor, raised a very pertinent question that none of the other doctors in the group had thought to ask.

How exactly was the position of the magnet supposed to be interpreted? The member of staff giving us the tour laughed. We would not believe, she told us, the amount of debate that this very question had generated among the health care professionals working in the building. Eventually, a consensus had been reached. “What you see is your current status within the building,” she explained.

I took this to mean that if the little black magnet was sitting over OUT, obscuring the word, then IN remained visible. The person was therefore inside the building and would need to be accounted for in the event of a fire drill or an actual emergency. That seemed straightforward enough. Except the doctor who had asked the question and another colleague promptly moved their magnets from OUT to IN. They were standing inside the building while the board was now effectively declaring that they were out. They had understood the explanation in precisely the opposite way.

My colleague from a few days earlier was standing beside me. He looked at what had just happened and muttered, almost rhetorically: “Why would they design something that is so confusing?” The member of staff who had given us the instructions looked at the board for a moment, her eyebrows drawn together, perhaps slightly perplexed by what had just happened. Then, with a smile, she explained it again. The magnets needed to sit over OUT, so that IN remained visible. The error was corrected in good faith, and we carried on with the tour.

But my colleague’s question stayed with me: Why would they design something that is so confusing? By this point, several doctors had interpreted a board containing only two possible states in two different ways. More importantly, judging from what we had just been told, we were far from the first people to do so. Perhaps, then, the problem was not simply that people kept misunderstanding the board. Perhaps the board was remarkably easy to misunderstand. Both interpretations, after all, make a certain amount of sense.

Place the magnet over IN, and the magnet could be understood as a marker: I am in. Place the magnet over OUT, however, and it could equally be understood as obscuring the option that does not apply: I am not out, therefore I am in. Once the convention is explained, it is easy enough to remember.

But if a system designed to communicate just two possibilities can repeatedly generate two entirely different interpretations, perhaps the more interesting question is not why people keep getting it wrong. Perhaps it is why we expect them not to. In health care, that question matters.

We work within systems considerably more complicated than a board containing the words IN and OUT. We prescribe through electronic systems. We interpret charts, labels, alerts, and symbols. We use medical equipment and navigate electronic records. We hand over information between teams, often while tired, distracted, or juggling several competing demands.

When something goes wrong, it can be tempting to focus immediately on the person involved. They should have paid more attention. They should have remembered. They should have known. And sometimes, of course, individual responsibility matters. But when several competent people independently make the same mistake, perhaps that mistake is telling us something about the system as well.

This is one of the ideas at the heart of human factors in health care: Rather than designing systems for an imaginary person who never becomes tired, distracted, or confused, we should recognize how real human beings actually interact with the environments we create for them. Good design should make the correct action as intuitive as possible. And ambiguity matters because the consequences of misunderstanding a system in health care can extend far beyond having one’s little black knight sitting in the wrong place.

Thankfully, nothing dramatic happened that afternoon. Nobody was harmed. Nobody was chastised. A few magnets were moved, an explanation was repeated, and we continued with our induction.

I suspect that now I understand the convention, I will remember it. Every time I arrive at work, my little black knight will obscure OUT, leaving IN visible. When I leave, it will do the reverse. But I suspect I will also remember my colleague standing beside me and asking a deceptively simple question: Why would they design something that is so confusing? Perhaps it is a question worth asking more often in health care. Because when intelligent people repeatedly misunderstand something we have designed, telling them to be more careful may not always be the answer.

Sometimes, we should look again at the design.

Loshi Rajen is a psychiatrist in the United Kingdom.